Radiation-emitting components are found in a large number of fields of use, inter alia for illumination and signalling purposes. Such components can be light-emitting diodes (LED for short) or organic light-emitting diodes (OLED for short). The latter can be produced inexpensively using thin film technology. When using a flexible substrate, for example, plastic such OLEDs are flexible or bendable.
OLEDs are constructed from a plurality of layers, for example, as a layer sequence of a substrate layer, a thin film encapsulation layer (TFE layer for short), an electrode, functional layers, that is to say emitter layer and hole-conduction layer, an electrode, a thin-film encapsulation layer and a protective layer.
Alternatively, an encapsulation cover can also be provided on an OLED without a thin film encapsulation layer and a protective layer arranged thereon that enables hermetic sealing of the active OLED layers and mechanical protection.
Bendable OLEDs can also be mounted in curved form. However, this leads to components encapsulated in the planar state and then bent, that have stresses in the component, especially at the interface between the OLED and the encapsulation cover. The stresses are accompanied by large restoring forces and can lead, inter alia, to delamination of the encapsulation cover and the holder. In particular, an OLED having an encapsulation made of flexible glass can be handled only with difficulties because of cracks associated with deformation of the glass. Such cracks cannot be completely avoided even by tempering, that is to say by heating of the material. There has hitherto not been a solution to the problem of the strong restoring forces that occur.
A possible field of use of bendable OLEDs is the automotive sector, in which OLEDs are used, for example, in driving direction indicators or as interior lighting.
To homogenize the temperature distribution and thus also the luminance distribution of OLEDs during operation at high luminous densities, in particular also in monochrome applications, for example, for red tail lights in the automobile sector and similar applications, a heat-distributing film is applied to the rear side of the OLEDs. That film is also referred to as a “heat spreader”. The heat-distributing film also leads to a homogenization of the aging process.
In flexible OLEDs on plastic film carriers, a heat distribution by such a heat-distributing film is likewise necessary since the lateral thermal conductivity of the plastic film or the organic protective layers or plastic protective layer is not sufficient to distribute the heat in a sufficient manner within the component.
For use in particular in the automotive sector, integration of a heat-distributing region in a 2.5D or 3D module is important to achieve a homogeneous emission characteristic in combination with longevity. Integration of the heat-distributing region on the module plane is to take place without damage to the other OLED layers or mechanical stress on the different layers of the flexible OLED.
In OLEDs having a rigid glass substrate, integration of the heat-distributing region can already take place at the component level in that, for example, a heat-conducting film is laminated onto the rear side of the OLED. Such a film can be a 50 to 200 μm thick aluminum foil, copper foil, a graphite foil or the like. If such components are glued onto a plastic holder during the modulation, for example, the heat-distributing region is already integrated in the component.
2.5 D OLED modules can be produced by processing a flexible OLED in 2D form, which is then bent into the 2.5 D shape and glued into a 2.5 D component holder in a curved shape. If flexible OLEDs are applied to a metal foil (e.g. made of stainless steel, copper, aluminum or the like), then the OLED components have the heat-distributing region already integrated in the substrate. Since the modulus of elasticity of the metal foil is orders of magnitude greater than that of the organic functional layers, the organic protective layers and the plastic protective film, after bending the neutral fiber of this layer stack lies substantially in the center of the metal substrate. When the flexible OLED is bent, this leads to stress in the functional layers and in particular in the encapsulation layers. Therefore, the bending radii of such OLEDs on metal foils are limited to the range of a few centimeters and, as a result, the bending radii in the 2.5 D module are likewise limited.
The thinner the used metal foil, the smaller the bending radii can be achieved. Typical values for minimum bending radii of OLEDs on, for example, a 100 μm thick stainless steel foil (SUS for short, special use, stainless) are about 2 cm. If a thinner metal foil is used, this has a positive effect on the minimum bending radii that can be achieved. However, the thermal conductivity of such a metal foil is reduced accordingly. For OLEDs having a glass substrate for use as a back light in the automobile sector, for example, a 100 or 150 μm thick aluminum foil is used for heat distribution.
If flexible OLEDs are processed on a plastic film, as in OLEDs on glass, the heat-distributing region on the component level can be integrated onto the rear side of the OLED at the component level by laminating the heat-distributing region. If such plastic OLEDs are brought into the 2.5 D shape with, for example, a metal foil on the rear side, the physical behavior with regard to stress on the functional layers or the thin-film encapsulation layers is similar to that of OLEDs processed on a metal foil.
It could therefore be helpful to provide an improved component module having a flexible component and a method for the production thereof.